The present invention generally relates to piezoelectric laminates and their manufacture, and in particular concerns a method of manufacturing a piezoelectric laminate in which the piezoelectric layer may be poled after it has been bonded to a rigid substrate layer.
Piezoelectric laminates typically comprise a layer of piezoelectric material bonded to a rigid insulating substrate material by an insulating elastically stiff or rigid bond layer. Such laminates are widely used in the manufacture of piezoelectric transducer arrays. Typical applications include the formation of phased array ultrasonic transducers and as components of ink jet printheads.
The bond layer, which normally has a rigidity comparable with that of the piezoelectric material or of the ceramic or glass substrate, generally has to be formed at an elevated temperature above or possibly just below the Curie temperature of the piezoelectric material. If exposed to these temperatures, the piezoelectric material may lose or have its remnant polarization substantially reduced. As a consequence, the piezoelectric material cannot be effectively pre-poled before forming the bond layer. Poling therefore preferably takes place subsequent to the formation of the bond layer.
Conventionally, the assembled piezoelectric laminate is poled by establishing a poling field between a pair of metal electrodes applied to the opposite faces of the laminate. This poling configuration has heretofore required the establishment of an impractically large poling field to effect adequate poling in a reasonable time period. That is, because of the high dielectric constant of the piezoelectric material relative to that of the substrate, a relatively small portion of the poling field is applied across the piezoelectric layer. Consequently, the strength of the poling field must be increased by a relatively large factor to effect poling, but frequently the extent of increase required is simply impractical.